DESCRIPTION: In the field of osteoporosis, bone mineral density is well known to predict a persons fracture risk. Bone mineral density is high in adolescents and young adults and falls throughout adult life and, as it falls, fracture risk increases. It is possible that cartilage thickness and volume represent the articular equivalent of bone mineral density. Cartilage thickness in the knee joint declines with age, just as symptomatic osteoarthritis develops with age. However, it is unknown whether cartilage thickness per se influences the development or progression of osteoarthritis in a joint The overall objective of this project is to investigate cross-sectionally a series of questions related to articular cartilage thickness in knees from a population-based sample of persons from the Framingham Study. We will study a random sample of knees from the population to obtain normative data and test whether trophic factors such as physical activity affect cartilage thickness. We will compare randomly selected nondiseased knees with nondiseased knees contralateral to affected ones and will take advantage of the notion that knees contralateral to those with disease represent knees at risk. We will evaluate the following specific aims: 1. To evaluate cartilage thickness in nondiseased knees, comparing knees contralateral to those with OA with knees drawn randomly from the population- Hypothesis 1. Cartilage is thinner in the contralateral knees of persons with unilateral arthritis than it is in nondiseased controls. 2. In those with osteoarthritis, to assess the relationship between recent and past physical activity and cartilage thickness. Hypothesis 2: Physical activity recently and habitually, is associated with an increase in cartilage thickness. 3. In those with and without radiographic osteoarthritis, to evaluate the association of cartilage thickness with knee pain. Hypothesis 3: In people with osteoarthritis and people without osteoarthritis, cartilage thickness is unassociated with the presence of knee pain. 4. To study the correlation of cartilage thickness with other known and putative risk factors for osteoarthritis. Hypothesis 4: Body mass index will be unassociated with cartilage thickness in nondiseased knees. Height will be positively correlated with thickness. Cartilage thickness will decrease with age and will be less in women than men. While these specific hypotheses will be addressed in this five-year proposal, this proposal and the MRI-based evaluation of cartilage thickness contained herein is a critical first step to a longitudinal study that will definitively test whether cartilage thickness is an important predisposing factor to osteoarthritis and whether its effect on osteoarthritis occurrence can help us understand how risk factors for disease affect the knee. This project will provide baseline assessments for this longitudinal evaluation. This study will be conducted as an ancillary project to the recently funded Framingham Osteoarthritis study in which comprehensive risk factor assessment will occur again and in which conventional MRIs of the knee are being obtained. We propose here to obtain and fund the acquisition and analysis of extra pulse sequences to allow us to measure cartilage volume and thickness in subjects undergoing MRI so that we can begin to address the questions posed here.